1. Field of the Invention
The present invention relates to a hot-press cushion material and its manufacturing method. More particularly, the present invention relates to a cushion material used when an object is press formed or hot pressed in a manufacturing process for a precision apparatus component (referred to as “laminated plate” in the present invention) such as a copper clad laminated plate, a flexible printed substrate, a multilayered printed substrate, an IC card, a liquid crystal display plate, and a ceramics laminated plate, and a manufacturing method of the above cushion material.
2. Description of the Background Art
When the laminated plate such as the printed substrate is manufactured, at the step of press forming or hot pressing, a laminated plate material 2 to be pressed is sandwiched between heating platens 3 and 3 as heating and pressing means and certain pressure and heat are applied to it as shown in FIG. 1. In order to provide a high precision formed product, it is necessary to apply heat and pressure to the laminated plate material 2 uniformly over the whole surface in the hot pressing. In this respect, the hot pressing is performed with a flat cushion material 1 interposed between the heating platen 3 and the laminated plate material 2.
Here, the general characteristics required for the cushion material 1 include cushion characteristics for absorbing the irregularities of the heating platen 3 and the laminated plate material 2, in-plane uniformity for transmitting the heat and the pressure from the heating platen 3 to the laminated plate material 2 uniformly over the whole pressing surface, heat conductivity for transmitting the heat from the heating platen 3 to the laminated plate material 2 effectively, heat resistance resisting against the pressing temperature and the like.
Conventionally, the hot-press cushion material 1 has been formed by laminating 3 to 20 pieces of kraft paper or linter paper in many cases. The paper cushion material is inexpensive and has balanced material properties in view of the cushion characteristics, in-plane uniformity and heat conductivity. This is considered that the fact that paper contains an appropriate void contributes to the cushion characteristics, the fact that the fibers constituting the paper are oriented in almost plane direction contributes to the in-plane uniformity, and the fact that the thickness of one piece is as small as 0.1 to 1 mm contributes to the heat conductivity. However, the paper cushion material has disadvantages such that the void cannot be restored after the pressing and the constituent fiber deteriorates by heat, so that it cannot be used a plurality of times repeatedly.
Meanwhile, as the hot-press cushion material that can be used repeatedly, there are various kinds of materials such as organic or inorganic fibers bound by a binder, a rubber, a unwoven fabric, a laminated body of rubber and unwoven fabric.
Japanese Unexamined Patent Publication No. 4-361012 (patent document 1) discloses a hot-press cushion material in which webs and fabrics are laminated alternately and needling-joined and a needlepunched unwoven is impregnated with a heat-resistant resin and heated and pressed so that its density may be within a range of 0.6 g/cm3 to 0.9 g/cm3. Here, the unwoven is formed of a meta-aromatic polyamide fiber, hemp (ramie), and polyester, and as the heat-resistant resin, a silicone rubber, an ethylene acrylic rubber and an EPDM are used. According to the patent document 1, it is said that even after the cushion material is used repeatedly for the pressing a plurality of times, its cushion characteristics can provide temporal stability by defining the density within the above specific range.
However, according to the needlepunched unwoven used in the Japanese Unexamined Patent Publication No. 4-361012 (patent document 1), unlike the paper manufactured through wet processing, since the fibers are mechanically joined by needling the webs through dry processing, the density of the web itself is not uniform. Therefore, the hot-press cushion material comprising the needlepunched unwoven has disadvantages such that the in-plane uniformity for transmitting the temperature and the pressure uniformly is inferior to that of the paper cushion material. Furthermore, the needlepunched unwoven has disadvantages such that it becomes thick inevitably because it is needled in a thickness direction, that is, in the case of the hot-press cushion material disclosed in the Japanese Unexamined Patent Publication No. 4-361012 (patent document 1), for example, its thickness is as long as 3.3 mm to 3.7 mm finally, so that the heat conductivity is not good. Furthermore, according to the hot-press cushion material disclosed in the Japanese Unexamined Patent Publication No. 4-361012 (patent document 1), since the needlepunched unwoven is impregnated with the heat-resistant resin and then heated and pressed, its void ratio becomes small, so that the cushion characteristics is not improved so much. That is, according to the hot-press cushion material disclosed in the Japanese Unexamined Patent Publication No. 4-361012 (patent document 1), in order to temporally stabilize the material properties after used repeatedly, the in-plane uniformity, the heat conductivity and the cushion characteristics are sacrificed.
In addition, Japanese Unexamined Patent Publication No. 9-277295 (patent document 2) discloses a hot-press cushion material in which a heat-resistant fiber base material having a thickness of 0.1 to 10 mm is impregnated with a fluoro rubber, silicone rubber or butyl rubber and the heat conductivity in the thickness direction is set to 4.0×10−4 cal/cm/sec/° C. or more. Here, the heat-resistant fiber base material includes a stainless needle felt, mat-shaped unwoven of carbon fiber, unwoven of glass fiber and the like.
The object of the invention according to the Japanese Unexamined Patent Publication No. 9-277295 (patent document 2) is to improve the heat conductivity. However, the hot-press cushion material disclosed in the Japanese Unexamined Patent Publication No. 9-277295 (patent document 2) has disadvantages that since it is impregnated with a lot of rubber, that is, 3 to 10 kg per square meter of the fiber base material having a thickness of 0.1 to 10 mm, the void of the fiber base material is filled with the rubber almost completely, so that its cushion characteristics deteriorates considerably. That is, according to the Japanese Unexamined Patent Publication No. 9-277295 (patent document 2), in order to improve the heat conductivity, the cushion characteristics is sacrificed.